How to mentally multiply big numbers

TL;DR

Learn how to multiply numbers using rounding, a simple and efficient method.

Transcript

good day today we're going to be having a look at a great way of multiplying two numbers together using rounding I'll start with an example 21 multiplied by 143 now as I said we're going to be using rounding to multiply these two bad boys so let's start with that so our first number that we have here is 21 that rounds pretty simply to the nearest 1... Read More

Key Insights

• 🎚️ Rounding can simplify multiplication by reducing numbers to more manageable levels.
• #️⃣ The rounding method involves finding the differences between the original numbers and their rounded counterparts.
• 🪜 Multiplying these differences and adding them to the rounded number helps in obtaining the final product.
• 💻 The units digit or the difference between the original digits can be used to compute the final answer.
• ✖️ The rounding method is a useful trick to multiply two numbers quickly and efficiently.
• 🛝 Understanding the steps involved, such as rounding, calculating differences, and multiplying, is essential for successful application.
• 🍵 Negative numbers can be handled using the rounding method as well.

Questions & Answers

Q: How do you start multiplying using rounding?

To start multiplying using rounding, round the smaller number to the nearest 10 and the larger number to a multiple of the rounded smaller number.

Q: What do you do after rounding the numbers?

After rounding the numbers, calculate the difference between the original numbers and their rounded counterparts.

Q: How do you find the answer using the rounding method?

Multiply the difference of the smaller number by the rounded larger number and add it to the rounded larger number. Then, multiply the result by the rounded smaller number. Finally, multiply the differences between the original numbers to get the units digit and add it to the previous result.

Q: Can you provide an example of multiplying using the rounding method?

Sure, let's use the example of 34 multiplied by 152. After rounding, we have 30 multiplied by 5. The differences are 4 and 2. Multiplying 4 by 5 gives us 20, which we add to 152, resulting in 172. Then, multiplying 30 by 172 gives us 5,160. Lastly, multiplying 2 by 4 gives us 8, which we add to our result, resulting in 5,168.

Summary & Key Takeaways

• The video demonstrates how to multiply two numbers using rounding as a method.

• Step 1: Round the smaller number to the nearest 10, and round the larger number to a multiple of the rounded smaller number.

• Step 2: Calculate the difference between the original numbers and their rounded counterparts.

• Step 3: Multiply the difference of the smaller number by the rounded larger number and add it to the rounded larger number.

• Step 4: Multiply the result from step 3 by the rounded smaller number.

• Step 5: Multiply the differences between the original numbers to get the units digit and add it to the previous result.